A semiconductor device, such as a transistor and a diode, using a nitride semiconductor operates at a high voltage and exhibits a high electric current density compared with a conventional semiconductor device. Therefore, the output power density and the operation frequency of the device can be raised, which allows such a device to be used in power control or to be used as a high frequency power amplifier.
However, this device suffers from a failure mode in which a drain current decreases due to the crack formed in an AlGaN layer. The crack is considered to be generated at the gate edge of the FET (Field Effect Transistor) due to the piezo-electric phenomenon. That is, when a voltage is applied between a gate and a drain, the strength of the electric field becomes large at the gate edge on the drain side. Then, the large electric field at the gate edge increases the stress due to the piezo-electric phenomenon, resulting in the crack.